(1) Field of the Invention
The present invention relates to an electrostatic image forming apparatus. More particularly, the present invention relates to an electrostatic image forming apparatus in which a toner image can be directly formed by a digital signal without optical scanning or corona charging.
(2) Description of the Prior Art
An electrophotographic process is generally used for forming an electrostatic image. For example, a photosensitive plate having a photoconductive layer is uniformly corona-charged and the plate is exposed imagewise to light by optical scanning to form an electrostatic image corresponding to the original image. Then, this electrostatic image is developed with toners charged with a polarity reverse to the polarity of the electrostatic image and the toner image is transferred to a copy sheet to obtain a print. Optical scanning exposure is indispensable for the electrophotography, and the sensitivity is limited because of the photoconductive layer used. Accordingly, the electrophotographic process is still insufficient in that the speed of forming prints cannot be highly increased.
As the conventional method for forming an electrostatic latent image based on electric signals, there is known an electric recording method in which a dielectric material is used for the recording layer, a needle electrode and a confronting electrode are arranged so that the dielectric recording layer is sandwiched between the two electrodes, and a recording signal is applied between the two electrodes. This method, however, has a defect concerning the image quality. For example, tailing is readily caused. Therefore, this recording method is not widely adopted at the present.
Furthermore, the charging operation is generally necessary in the conventional image forming processes. If a toner image can be directly formed by a digital signal or image signal without optical scanning or corona charging, a great operational advantage will be attained.